Method of rolling threads



Dec 5, 1944. 'J. H HOERN METHOD OF ROLLING THREADS 2 Sheets-Sheet l- Filed June 4, 1945" INVENTOR A TTORNE Y Dec. 5; 194 4.

4. H. HOERN 25643442 METHOD OF ROLLING THREADS Filed June 4, 1945 2 Sheets-Sheet 2 ATTORNEY$.'

Patented Dec. 5, 1944 METHOD or ROLLING THREADS Joseph H. Hoern, Birmingham, Mich., assignor to Eaton Manufacturing Company, Cleveland,

Ohio, a corporation of Ohio Application June 4, 1943, Serial No. 489,639

13 Claims.

This invention relates to the rolling of screw threads on machine parts such as bolts, screws and the like by means of flat dies and has for its principal obect the provision of a method of rolling threads in' this manner by the practice of which threads may be produced on a part as accurately as has heretofore been possible by grinding operations.

Objects of the invention'include the provision of a method of rolling'screw threads on apart to be provided therewith by the practices of which threads of an extremely accurate character may be formed within extremelyclose tolerances; the provision of a method of rolling screw threads on a part between flat dies by the practices of which the possibility of metal overlapping in the threads of the work is effectively eliminated; the provision of a method as above described in which perfect alignment of the threads on the dies with respect to the threads being formed on the work is assured at all times the pro-vision of a method as above described in which diametrical distortion of the body of the work under the force of the dies is effectively eliminated, and the provision of a method of rolling screw threads by flat dies in which the life of the dies ismaterially extended as compared with those employed in conventional methods.

Other objects of the invention include the provision of a method of rolling screw threads on .workpieces by means of flat dies including the steps of insuring initiation. of the rolling movement of the work between the dies when the dies are in a predetermined position with respect to each other in the direction of their movement longitudinally with respect to each other, by first efiecting only partial imbedding of the dies in the work and thereafter effecting a complete imbedding ofv the dies in the work; the provision of a method as 'above described in which the final imbedding of the dies in the work is accomplished radually; the provision of a method as above described in which the final imbedding of the dies in the work is accomplished by a bodily shiftable movement of one of the dies laterally with respect to the other thereof; the provision of a method as above described in which the dies are separated from one another prior to the time the workpiece is discharged from between them; the provision of a method as above described in which the dies are initially separated from one another by a distance greater than that required to form complete threads on the work but less than the external diameter of the work blank, initiation of the rolling movement of the work between the dies is effected while the dies are so laterally separated from one another, and then the dies are caused to laterally approach each other tocomplete the imbedding thereof in the work; the provision of a method as above described including the step of initially locating the workpiece centrally between the two frelatively movable die parts prior to gripping the workpiece between such parts; and the provision of a method of rolling threads as above described in which the relative movement of the die parts laterally with respect to each other is effected by the use of fluid pressure.

Still further objects of the invention include the provision of a new and novel method of checking the steps of initially efiecting a partial imbedding of the dies in the work and then checking the alignment of the relatively shallow grooves thus formed in the work; and the provision of a method as herein described in which the alignment of the relatively shallow grooves is checked by the use of an optical projector.

Additional objects of the invention include the provision of a method of rolling threads between substantially flat dies in which the dies are moved longitudinally relative to each other at a constant speed whereby to result in better work and longer life of the dies than in accordance with conventional methods; and the provision of a method in which the speed of operation of the dies may be simply varied to enable the highest safe speed of operation to be maintained between the dies and the work commensurate with the hardness of the work and the practical life of the dies.

step or steps of operation to be hereinafter described with reference to the accompanying drawings, and then claimed, having the above and other objects in view.

In the accompanying drawings which illustrate more or less diagrammatically apparatus by means of which themethod of the present invention. may be carried out, and the association of the work therewith,

Fig. 1 is a fragmentary, broken and partially sectioned plan view of threadrolling apparatus invention may be carried out, and illustrating a piece of work in operative relation with respect thereto;

Fig. 2 is an enlarged fragmentary, plan view of that portion of the apparatus shown in Fig. 1 within the circle 2 thereof;

Fig. 3 is a vertical sectional view taken on the line 3-3 of Fig. 2 and illustrating the work in the position which it assumes with respect to the thread rolling dies at the. moment that initiation of the thread rolling movement .of the dies on the work begins;

Fig. 4 is a view similar to Fig. 2 illustrating the use of a modified and preferred form of die structure employed in the method;

Fig. 5 is an enlarged, fragmentary sectional View taken on the line 55 of Fig. 4 and illustrating the conformation of the threads of the dies at the advanced ends thereof;

Fig. 6 is a more or less diagrammatic view illustrating the manner in which an optical projector is employed to check the accuracy of the alignment of the dies by employing a workpiece in which the dies have been initially engaged only;

Fig. 7 is a side elevational view of a typical form of workpiece in blank form; and

Fig. 8 is a side \elevational view of the workpiece shown in FigL-7 after it has been threaded.

In the conventional method of rolling threads on workpieces between flat dies, thedies are located laterally with respect to each other at such a distance that when a workpiece is passed between them it will be'provided with threads of the desired pitch diameter, the dies are caused to relatively reciprocate with respect to each other longitudinally thereof and each time the movable diemember is separated from the stationary die member at one end of its stroke the workpiece is fed into position and is gripped between the two die members on the ensuing stroke and acted on thereby to form threads thereon. While the advanced ends of the dies are usually curved outwardly away from the plane of the threaded face thereof and the threads of the dies are curved outwardly therewith, nevertheless it will be appreciated that the dies in operation are sunk almost immediately to full depth in the work. I have found that where accuracy in the final product is important this is undesirable for several reasons. because of the .almost immediate sinking of the threads of the dies into the work, an effect is produced similar to a heavy blow which is often sufilcient not only to displace the surface-metal of the workpiece from which the threads are to beformed but to actually deform the entire body of the workpiece throughout its full diameter. Egg-shaped sections of the work often result from this cause. Furthermore, because of the almost immediate sinking of the threads of the dies into the workpiece by such practice and the resistance offered thereto, the workpiece often One reason is that,

slips with respect to the dies with the result that i from the plane of the operative faces thereof and the threads of the dies are carried outwardly "therewith, unless the threads are a so p p curved transversely of such curved advanced ends, the impressions formed thereby in the workpiece will not be at the same-helix angle as the impressions formed by the straight threads on the, dies over the flat portion thereof and introduce errors into the work for this reason.

Another disadvantage of rolling threads on screws or the like in accordance with conventional practice is that when the work is first introduced between the dies it often becomes imbedded to a greater extent in one of the dies than in the other and this defect carries through the complete thread rollingoperation with the result that in such cases the threads on-one side of the screw or bolt are deeper than those on the other side thereof and the outside diameter of the threaded portion of the screw or bolt is not concentric with the axis of the pitch diameter of the threads. Under such circumstances it will be appreciated that the head of the bolt having been concentric with that portion of the blank on which the threads have been formed, the head of the bolt is not concentric with the outer diameter of the threaded portion of the bolt in the final product and this leads to many disadvantages in practice. Apparently one of the reasons whythis condition occurs is that due to the outwardly curved entering end portions of conventional thread rolling dies and the absence of means for holding the work centrally between the dies at the moment it becomes engaged by them, there is a tendency for the work. or at least the work is capable of being, imbedded to different distances in the dies when first gripped between the curved end portions thereof.

The inaccuracies resulting in the threads produced on workpieces in accordance with conventional practice as heretofore followed has resulted in threads of such inaccurate character that generally such workpieces, i. e., bolts. screws, or the like, are usually accepted for only the roughest kind of work and are not permitted to be used in the better class of mechanisms such as machine tools, engines, and devices where even more accuracy of fit is required. At

the present time great quantities of accurately formed screw elements are being used. In many of these screw elements the tolerated variations from the true pitch diameters are 0.003" or less in which case, in order to obtain screw threaded elements within such limits and ones which have the desired smooth thread surfaces, it has been necessary to grind such threads, which operation involves. a relatively great expense. If such accurately threaded screw elements could .be threaded by means of dies so as to eliminate the grinding operation, the cost of forming such threads would be a small proportion involved in forming such accurate threads in accordance with conventional practice.

It is, therefore, the principal object of the in-- vention to provide a method by the practice of which the threads of screw threaded parts may be formed by flat dies in such a manner that the accuracy and finish thereof are comparable to the accuracy and finish of threads now produced by grinding and may actually be employed for any use which ground thread parts of extreme accuracy are used. The above objects are obtained bythe use-of flat dies which not only are reciprocable longitudinally relative to each other in the same manner as in conventional methods, but further in which the dies are relatively movable withrespect to each other lat erally thereof. In this connection it is to be:

essence understood that when the term "relative move- .ment between the dies or equivalent expression is employed herein to refer to the movement of the-dies either longitudinally or laterally with respect to each other it is to be interpreted to mean movement of either one or both dies to effect such movement either longitudinally or laterally thereof, respectively. In this Connection it may be stated that while each' die may be movable toward the other both longitudinally and laterally it is preferable to fix one such case having relative movement with respect to each other in accordance with the definition given above.

Infollowing out the method of thewpresent invention, the dies are laterally spaced frdm one another atuthe time the workpiece or' blank is introduced between them by a distance greater than that required to form full depth or complete threads on the blank but by a distance less than the outside diameter of the blank itself, so that when the blank is first gripped between the dies during longitudinal movement of the latter the threads of the dies will'be only partially im bedded in the surface of the blank. This step is for the purpose of insuring rolling of the blank between the two dies the moment it becomes gripped between them, thus insuring against any possible slippage between the blank and the dies. which slippage would throw the workpiece out of 1 synchronism with the threads of both of the dies and result in the disadvantages heretofore described. 11; will also be appreciated that, in order to maintain the synchronized condition between the work blank and the dies above referred to, and particularly where the movable die is moved by fluid pressure, it is necessary that initiation of the rolling movement of the blank between the dies must occur when the dies are substantially exactly in a predetermined relative longitudinal position with respect to each other during relative longitudinal movement between them, and the present invention contemplates the provision of stepsv by which this feature is assured. Furthermore, means are provided for accurately locating the blank midway between the dies at the moment of engagement thereof be tween the dies. This feature combined with the fact that the threads on the advanced ends of the dies are preferably not curved outwardly as in conventional practice, insureseven imbedding ofboth dies in the work and eliminating the offcenter relation between the outside diameter and pitch diameter of the threads so often occurring in screw threaded parts formed by conventional practice.

In accordance with the present invention, the partial imbedding of'the teeth of the dies in the work preferably conntinues after initiation of the rolling movement of the work blank between the q dies for at least half a turn so that a continuous but partially formed thread is formed in the work blank thereby. Upon the attainment of such condit1on and during the relative longitudinal movement of the dies with respect to each other, the dies are moved, more or less gradually, laterally toward one another. In view of the fact that the dies have already acted upon the work blank :to partially form the threads therein, and particularly where the dies are moved laterally'toward one another more or less gradually, the sudden imbedding or the dies occurring in accordance with conventional practice to full .depth in the workpiece does not occur by-the 'practices of the present invention and the liability of slippage between the dies and the work blank is, therefore, effectively eliminated. This insures, assuming, of course, that the dies have been accurately formed, a truly helical thread on the workpiece which is free irom overlapping of metal and, in fact, of a superior finish to that normally obtained by a grinding operation.

Although, under the above described condi: tions, after the initially imbedded threads of the dies have formed partial threads in the work blank and have been moved laterally toward one another to the apparent extent of such movement, it has been found that, due to the resistance offered by the'work-piece to the complete imbedding of the threads of the dies therein, the

inherent yield of the mechanism employed to advance the dies toward one another and of the machines employed prevents complete sinking of the dies into the work until more than one revolution of the work has occurred under such conditions and the metal of the workpiece has had a chance to flow under the pressure of the dies to assume its final condition. This latter feature is especially important where the tolerated variations of the dimensions of the workpiece are small. It is also important, where the character of the finish of the threads on the workpiece is important, to laterally separate the dies from one another before the workpiece has reached the end of at least one of the dies and has been discharged therefrom, otherwise one or both dies, depending upon the point at which the workpiece becomes disengaged from between the dies,

may leave an imprint of its end surface on the sirable in that in accordance with a further phase of the present invention the force exerted by such fluid pressure means is preferably such as to be incapable of completely sinking the threads of the dies into the workpiece while the dies and workpiece are stationary, but is suf ficiently great so that during the continued rolling movement of the workpiece between the dies, the dies are more or less gradually sunk home to their final position. This feature not only provides the gradual sinking of the threads of the dies into the workpiece; but further acts as an aid. in.insuring against slippage between the dies and the workpiece because of such rapid sinking of the dies into the workpiece as to engender danger of slippage between the workpiece and the diesand, therefore. throwing the workpiece out of synchronism with the dies.

" Referring now to the accompanying drawings. in Fig. 8 is shown a typical screw which may be advantageously formed inaccordance with the method of the present invention. It is to be understood that the screw shown in Fig. 8 is arbitrarily selected from a large class of screws or other threaded elements that may also be advantageously formed in accordance with the present inventionand is selected in this case simply as a matter of illustration. It will be noted that the screw illustrated in Fig. 8 includes a threaded end portion joined at one end to a shank l2 of a diameter preferably slightly less than the root diameter of the threads on the end l2. The shank I2 is enlarged at that end thereof opposite the threaded end l2 as at M to approximately the outside diameter of the threaded end I0 and joins with a concentric disc-like flange IS on the opposite face of which the usual head i8 is formed. The work blank from which the screw shown in Fig. 8 is formed in accordance with the present invention is illustrated in Fig. 7 generally by'the I of the usual V-type, then the diameter of the end ID of the workpiece or blank I will be sub-- stantially equal to the pitch diameter of the threads in the final workpiece. The tolerance or permitted variation of the dimensions in the end H) of the work blank I will, of course, de-

pend to a certain extent upon the tolerances permitted in the finished workpiece, although greater tolerances are always permitted in the diameter of the end I0 than in the pitch diameter of the finished piece inasmuch as the outside diameter of the threads formed is not of greatimportance andis desirably terminated short of a perfect point. Rather, it is of major importance in the forming of the blank! that the end 10' is of such diameter that the metal thereof will not completely fill the threads of the dies to the very roots thereof for it will be appreciated that if the diameter of the end l0' of the workpiece or blank 1 is so great as to provide more metal than is required to completely maker.

for the change in the helix angle caused thereby and which lateral curvature is always a matter of more or less guesswork on the part of the It may be noted that, principally for the purpose of more clearly bringing out certain desirable features of the present invention, the advanced ends of'the dies and 22 in the direction of their relative movement with respect to each other during a working stroke are shown as being square with respect to the plane of the threaded faces thereof, whereas in actual practice it is preferable to bevel oil the outer end teeth of such entering ends of the dies as illustrated in Fig. 4 and as will hereinafter be more specifically. described. For the present, it will be sufficient to consider that the entering end faces of the dies '20 and 22 join with the threaded .faces of the dies through a sharp corner or fill the space between the threads of the dies,

the only avenue of escape for such excess metal is in a direction parallel,with the faces of the dies and intermediate the two dies, thus causing. the final workpiece to be egg-shaped in cross section.- Otherwise the precautions necessary in making the blankl are not at all-unusual.

In order to form the workpiece shown in Fig. 8 from the blank 1 shown in Fig. 7 in accordance with the method of the present invention, a pair of dies, illustrated in Figs. 1 to 3, inclusive, at 20 and 22, respectively, are employed. The dies 20 and 22 may be more or less of conventional character having, as illustrated in Fig. 3,

1 threads 24 formed on their opposed faces complementary in section to the section of the threads desired on thejworkpiece-andmf course,

disposed at an angle to the horizontal equivalent to the helix angle desired in the workpiece. The

- height of the threaded portions of the dies is preferably only slightly in excess of the length of the end 10' of the blank and the dies 20 and 22 are extended upwardly from the threads 24 such a distance, as brought out in Fig. 3, that the flange IS, in resting upon theupper edges of the dies, serves to locate the end I0 in proper relation with respect to the threads 24.

The principal difference between the dies 20 and 22 and conventional dies is that preferably the roots of the threads 24 in each die lie in a in points as illustrated in Figs. 1 and 2.

-While the mechanism employed for moving the dies 20 and 22 relative to each other both longitudinally and laterally thereof may be of any, suitable character in accordance with the broadsupported against lateral movement particularly a in a direction away'from the die 22. The head 26 may be caused to reciprocate in any desired manner but, in accordance with a more limited phase of the invention, it is shown as being connected to the piston rod 30 of a piston 32 reciprocably received within a cylinder 34 mounted" upon the machine with its axis parallel to the path of movement of the head 26. It may be assumed that the piston 32 is caused to operate in the cylinder 34 by means of fluid and preferablyliquid under pressure introduced through a conduit 36 equipped with a throttle valve 31 to a control valve 38 from which tubes 40 lead to the opposite ends of the cylinder 34 and from which and exhausted-from the opposite end and whenat the opposite end of its movable position the flow of fiuid will be reversed.

The importance of employing a hydraulic piston and cylinder assembly for moving the die 20 longitudinally with respect to the die 22 is as follows. In the past it has been conventional practice to 'move one die with respect to the other by a crank arm and pitman construction with the result thatthe speed of the movable die var-' ies in accordance with the point of connection of the pitman with the crank pin on the crank pin circle, the dies moving relatively slowly with respect to each other when the work is first engaged between the dies, then increasing to a maximum extent at the time the length of the pitman is at right angles to a line connecting the crank pin to the axis of rotation of the crank arm, and then decreasing toward the end of the stroke. The crank is ordinarily rotated at the fastest speed possible at which the dies will satisfactorily stand up for a workpiece of average hardness but in such case the speed of relative movement between the dies is either much lower than necessary at the beginning and end of the operation or else it exceeds the safe linear speed between the dies and the work during the central portion of each stroke and which in the latter case is detrimental to the life of the dies. Furthermore, it is extremely difficult, if not impractical, in most cases, to change the speed of relative reciprocation between the dies to accommodate them to work pieces of different hardnesses.

By employing a hydraulic cylinder and piston for effecting relative reciprocation between the dies longitudinally thereof it provides a constant speed of the dies relative to one another over the entire stroke and by employing a throttle valve such as 31 controlling the volume of flow through the inlet pipe 36 the relative speed of reciprocation between the dies may be varied so as to maintain the highest safest speed in every case. In other words the speed of reciprocation may be varied by the valve 31 so that the speed of the dies is the fastest practically possible for any given piece of work with due regard to the, life of the dies.

the speed of reciprocation 'may be adjusted through the valve 31' to correspond. In this connection it will be appreciated that the'softer the metal the higher the permissible linear speed between the dies and the work, and the harder the material the smaller the linear speed desirspaced relation to each other on the rod 44 co-.

operate with an actuating member 50 secured to and reciprocable with the head 26 and extending into embracing relationship with respect to the rod 44 between the stops 48. Engagement of the member 50 with either stop 48 causes the rod 144 to be moved in the'direction of movement which the head 26 is then moving and acts through the valve arm 52 'to shift the valve 38 from one limit of its movable position to the pposite limit thereof, thereby to reverse the direction of movement of the head 26.

The die 22 is, of course, arranged with its threaded face in parallel relation with respect to the threaded face of the die 20 where the threaded endof the screw element to be formed is cylindrical and not tapered, but, of course, tapered where the latter condition obtains; In this connection, for the purpose of simplicity in description in the following specification and claims, it is to be understood that where reference, is made to the dies as having parallel faces and/or the blank as having a cylindrical portion to be threaded, it is to be interpreted broadly enough to relate to and to cover a condition wherein the faces of the dies are inclined into conformance with the taper of a tapered part to be threaded and in which that portion of the blank to be threaded is correspondingly tapered. The die 22 is shown fixedto the outer end of a relatively rigid piston or plunger 66 which is reciprocably received within a cylinder 62 rigidly fixed with respect to the bed of the machine and with its axis perpendicular to or substantially perpendicular to the plane of the threaded faceof the die 2i! The die 22 is thus mounted for When workpieces made from diiferent hardnesses of material are being worked upon movement in a direction perpendicular or substantially perpendicular to its threaded face and, therefore, laterally with respect to the die 20. Means are provided for limitin the movement of the die 22 laterally towards the die 20 and this is shown more or less diagrammatically in Fig. 1 as comprising a stud 64 threaded centrally into the outer end of the piston 66 and projecting outwardly through the blind end of the cylinder 62 where it receives a stop nut 66 and lock nut 68, the former being engageable with the outer end of the cylinder 62 to provide a stop for limiting outward movement of the piston 66 in the cylinder 62. It will be appreciated, of course, that where such a construction is employed, suitable packing means will be provided about the stud E4 in its passage through the blind end of the cylinder 62.

Means are also provided for constantly urging the piston 66 inwardly of the cylinder 62, in the present case this beingshown by way of illustration as comprising a pair of. springs disposed on diametrically opposite sides of the cylinder 62 and tensioned between a hook or the like 12 fixed to the rear face of the die 22 and another hook M fixed to the cylinder 62.

In accordance with the present invention, means are also .provided for limiting the lateral movement of the die 22 away from the die cally shown as consisting of a stop screw 16 threadably mounted in a lug 18 on the side of the cylinder 62 and arranged with its inner end in a position to abut the rear face of the die 22 when the latter has moved laterally away from the die 20 under the influence of the springs 10.

It will be appreciated that the stop nut 66 will be so positioned on the stud 64 as to limit lateral movement of the die 22 towards the die 26 to such a lateral spacing between the dies 20 and 22. as to result in the forming of threads on a work-piece engaged between the dies to the desired pitch diameter, the spacing of the dies 20 and 22 in such position being equivalent to the permanent spacing which these general types-of dies are spaced from one another in accordance with conventional practice. On the other hand the stop screw 16 will limit lateral movement of the die 22 away from the die 20, in accordance with the present invention, to a distance such that the points of the threads 24 on the dies 26 than the difference between the pitch diameter of the finished piece and the outside diameterof the end portion ID of the work blank or piece.

In Fig. 1 the die 22 is shown at the outer limit of its reciprocable position as determined by the position of the stop screw 76. The clearance between the stop nut GB and stud 64 and the end ,voir or the like, and a tube 88 with the outer end of the cylinder 82. The valve 88 is provided with an actuating handle 88 which, when at one extremity of its movable position, connects the tube 88 with the tube 82 and, when at the opposite end of its movable position, connects the'tube 88 with the tube 84.

- Any suitable means may be provided for operating the valve 88 in-timed relation with respect to the longitudinally reciprocable position of the piece at the time the dies first grip it between them is exerted in a plane passing diametrically through the workpiece, thus reducing the tenddie 28. In the particular case shown by way of illustration, this means comprises a solenoid unit 88 connected by a link 98 to the free end of the operating handle 88 of the valve 88. The solenoid unit 89 is connected in series in an electrical circuit with a conventional switch 92 mounted on the frame of the machine and having an actuating arm 84 positioned in intersecting relationship with respect to the path of movement of the head 28 on the ways 28. As will hereinafter be more fully explained, the switch 82 is so positioned in the path of movement of the head 28 that the work will be gripped between the dies 28 and 22 while the dies 28 and 22 are at the extreme outer limit of their relative movement in direction lateral to their operative faces before the head 28 engages the switch 82 to connect the tube 82 with the tube 88 and thus move the dies 28 and 22 to the inner limit of the relative lateral movement with respect to each other. Where the die 28 continues to move longitudinally in the same direction, the head 28 will pass beyond and become disengaged from the-switch 82, thereby causing the switch 92 to beoperated to disconnect the tube 88 from the tube 82 and connect it to the tube 84 and thereby separate the dies 28 and 22 laterally with respect to each other. This last separating movement of the dies preferably occurs before the work is discharged from between the dies so that the ends of the dies will not mark the work.

It will be appreciated that with the particular mechanism shown for controlling the movement of the die 22 laterally with respect to-the die 28, upon the ensuing stroke of the head 28 in a reverse direction as soon as the head 28 again engages the switch 92 the die 22 will be moved laterally towards the die 28, this during an inoperative stroke of the machine and, therefore,

not essential and ordinarily not desirable. It will Fig. 7, is introduced between the dies 28 and 22 in accordance with conventional practice and a reciprocable spring-pressed pusher rod I88 ofconventional construction is preferably provided for forcefully urging the work I8 into position between the dies at the initiation of the rolling operation. In accordance with the-present invention, however, it is desirable to so position the work I laterally with respect to the dies 28 and 22 that the pressure exerted on the workency towards relative slippage of the work with respect to the dies to a minimum at this time and to insure perfect synchronization of the rolling movement of the work with respect to the dies. In this connection it will be appreciated that the work must begin to roll when the dies are in a predetermined position with respect to each other if the threads formed on the work by the threads of both of the dies are to be exactly helically, aligned with each other and that if, for instance, the work should slip with respect to the dies, even to the slightest extent, the synchronized relation of the threads of the dies and the threads on the work will be destroyed and result either in drunken threads being formed on the work or threads in which the metal of the workpiece is overlapped, thus resulting not only in a weak thread but one which is inherently rough. At the same time this locating or positioning means is such as to locate the work midway between the dies at the moment it is gripped between them so as to insure an equal initial imbedding of both dies in the work. This leacis to continued equal imbedding of the dies in the work in the subsequent phases of operation and insures the outer diameter of the threads being concentric with the pitch diameter thereof in the final product.

To-thus locate the work I with respect to the dies 28oand 22 so that they will engage the workpiece I in a plane passing diametrically through the work and centrally thereof, a suitable stop is associated with the die 28 so as to limit the position to which the workpiece I may be projected or positioned with respect to the die 28 under the influence of the pusher bar I88 at the initiation of the forming operation. While any suitable stop means may be provided for this purpose, in the drawings by way of illustration such stop means comprises a bracket I82 rigidly fixed with respect to either the die 28 or the head 28 and provided with two or more stop screws I84 v vanced ends of the dies 28 and 22. By suitably adjusting the screws I 84, it will be appreciated that the workpiece, in simultaneously engaging the inner ends of the screws I84 and the advanced corner of the die 28, as illustrated in Figs. 1 and 2 in particular, will be limited in its inward movement with respect to the operative face of the die 28. The stop screws I84 are preferably so adjusted that the axis of the workpiece I will be located exactly midway between the opera tive faces of thedies28 and 22 when the dies 28 and 22 are separated laterally to a maximum extent as controlled by the stop screw I8 acting on the,

die 22. When this condition prevails, and as particularly brought out in Fig. 2, when the workpiece I is first gripped between the points of the dies 28 and 22 during reciprocatory moveaseame cated at I06 which passes through the axis of the workpiece I and the workpiece I will be positioned exactly midway between the dies, resulting in a condition in which the tendency of the workpiece I to slip relative to either the die other is preferably about only that which will insure immediate rotation of the workpiece when engaged by the dies. Obviously, it will depend to a greater or lesser extent upon the diameter of the'workpiece and particularlythe diameter of the portion I thereof in the particular workpiece shown. I have found it ordinarily advisable to imbed the teeth of the dies into the work during this initial stage of movement for a distance which may vary, in a workpiece having a diameter equivalent to the diameter I0 of the workpiece shown in Fig. .7 of from one-half inch to one inch, somewhere between 0.005" and 0.015", and even to a greater depth in some cases, a distance of 0.010" having been found quite satisfactory in service. Where sharp ended dies, such as illustrated in Figs. 1 and 2, are employed, then such initial imbedding of the dies in the work may be even less than that'stated.

In actual practice it will be appreciated that at the time the workpiece! is introduced against Y the stop screws I04, the die 20 will be withdrawn to the right from the position illustrated in- Figs. 1 and 2, the work being introduced against the stops IN, the pusher bar I00 moving forwardly to resiliently hold it in such position, and the die.20 will then move with the head 26 to the left as viewed in Figs. 1 and 2. As soon as the die 20 has moved to the left a sufficient distance to cause the workpiece I to be gripped between the opposed leading edges of the dies 20 and 22, the workpiece I will begin to roll with respect to the dies, it rolling relatively rearwardly 0n the die 20 away from the stop screws I04. At this time, be cause the head 26 has not yet engaged the operating member 94 of the switch 92, no pressure will be exerted in the cylinder 62 and, consequently, the springs I0 will have moved the die 22 laterally outwardly to the outer limit of its movement away from the die 20. Consequently, the teeth 24 of the dies 20 and 22 will be imbedded a relatively small amount in the surface of the workpiece 'I, such distance as previously explained being sufficient to positively insure the desired rolling movement of the workpiece I with respect to both the dies 20 and 22 but insufficient to endanger relative slippage-of the work with respect to either of the dies. It is also important to' bear in mind that, because of the character-ofengagement of the work between the dies 20 and 22, the work will begin to rotate immediately and precisely at the moment the die 20 reaches a predies will, of course, form threads of only partial .depth in the workpiece and the longitudinal 10 the workpiece, the head engages the end 04 movement of the dies relative to each other-while thus separated is preferably continued until the work has rotated through at least one-half a revolution, and preferably to a greater angular extent so that such partial threadsformed thereby are continuous.

After such partial threads have been formed in of the switch 92, the effect of which is to immediately connect the pressure tube 82 of the valve 80 with the tube 86 leading to the cylinder. 02 upon which fluid underpressure is transmitted to the piston 60 to cause the die 22 to be moved laterally towards the die 20, thus to cause the by the pressure applied in the cylinder 02 to the threads of the dies 20 and 22 tobe imbedded to their full extent in the surface of the workpiece I. It is not desired that this movement of the die 22 laterally with respect to the die 20 be an instantaneous movement, in fact,,such type of movement is to be avoided inasmuch as any such sudden imbedding would increase the tendency of the Work to slip relative to the dies and increase the tendency of the dies 'to work the metal of the workpiece clear to its center and tend to distort the true section thereof. The movement of the die 22 laterally toward the die 20 is preferably of a more or less gradual nature so as to avoid the tendenciesabove referred to and so that substantially full imbedding of' the teeth of the dies in the workpiece will not occur until the workpiece has rotated to preferably in excess of a complete revolution and preferably from one to three revolutions While pressed between the dies. This more or less gradual inner movement of the die- 22 may be effected in any suitable manner, such as by restricting therate of flow of the liquid from the valve into the cylinder 62, but I have found it preferable, in accordance with a further phase of the invention, to control such movement piston 00 and this is accomplished in the following manner.

It will be appreciated, that if a chisel, and to which the teeth 24 of the dies 20 and 22 may be likened as a matter of illustration, is pressed against the surface of a stationary piece of work a relatively great amount of pressure will be reamount or im'bedding of the chisel in the work.

This same feature is preferably employed in effecting the gradual imbedding of the teeth of the dies 20 and 22 into the workpiece I. In other words, the amount of pressure which is applied to the piston 60 once the initial action of the dies on the workpiece iscompleted, is such that if the workpiece and dies were stationary, the pressure would be insufficient to effect the complete imbedding of the teeth of the dies into the work but, under the conditions actually existing, the rolling movement of the work between the dies in combination with the pressure employed is sufiicient to effect the substantially complete imbedding of the teeth 24 of the dies into the work during the number of revolutions of the work mentioned. Even then it has been foundin actual practice that when the stop nut 66 actually comes into firm engaging relationship with respect to the cylinder 22, or the equivalent condition results, the threads of the dies are not immediately imbedded in the work to the full extent desired because of the inherent resiliency that is present in all machines regardless of their apparent rigidity, and that further rolling movement between the dies and the work must be continued before it is insured that the threads of dies are completely imbedded to the desired extent in the work. Under ordinary conditions it is desirable that the work be caused to be rotated from three to seven or more times after the dies have apparently become fully imbedded in the work in order to positively eliminate the effects of the spring of the machine and to obtain the desired accuracy in the finished product.

It will be appreciated, of course, that the amount of pressure which is introduced into the cylinders 62 and/or the number of turns of the work under such pressure required to apparently fully imbed tne teeth of the dies into the work will vary according to the pitch and therefore the depth of the threads to be formed in the workfi-the diametcr of the work, the hardness of the metal of the particular workpiece being operated upon,

and similar obvious conditions.

As previously mentioned, it is preferable to separate the dies 20 and 22 laterally with respect to each other, prior to the time that the workpiece is discharged from between them, to a change in helix angle which would otherwise occur.

The amount which the advanced ends of the teeth 24 of the dies 20' and 22 are thus beveled is, as illustrated in Fig. 4, greater than the dis-- tance which the teeth 24 are initially imbedded in the workpiece 10 so that at the time the workpiece 1 is first engaged between the dies 20' and 22' it is engaged between the beveled surfaces 21. These beveled surfacs 2| being of the same angularity, and the stop screws I04 being adjusted to locate the workpiece I accurately midway between the opposed faces of the dies, it will be appreciated that in this instance the points of contact between the dies 20. and 22' with the workpiece! will be in a plane which, as in the first-mentioned construction, passes axially through the workpiece I as on the line I06 in Ill sufficient extent to relieve the pressure of the dies on the workpiece, as otherwise the trailing points of the dies might undesirably mark the workpiece. In the present instance shown, the

length of the head 26 is less than the combined length of the dies 20 and 22 so that the operative end 94 of the switch 92 will drop off the head 26 during an operative stroke of the latter before the workpiece is discharged from the ends of the dies, this separation of the dies 20 and 22 under such conditions relieving the pressure of the dies on the work and eliminating the possibility of any such marking.

In actual practice, it is usually undesirable that the dies such as .20 and 22, and particularly the teeth thereof, terminate in a square edge at their advanced ends, this for the reason that such square edges produce sharp points for initial engagement with the workpiece and these sharp points are subjected to unduly high pressures in operation which tend to foster early destruction thereof. In practice it'is preferable to bevel ff the teeth 24 of the die at the advanced end of the die so that the workpiece will be initially engaged by the beveled surfaces rather than the points. This is illustrated in Fig. 4 in of the dies 20 and 22' are not similarly beveled off and, as usually occurs in conventional constructions, the outer portions of the teeth 24 only being beveled in'this case. This is brought out in Fig. 5, which illustrates the initial contacting relationship between the die 22 and the workpiece 1 before imbedding of the die in the workpiece has occurred. This eliminates the ne-' cessity of attempting to laterally curve the beveled ends of the teeth to compensate for the 75 Fig. 4. Thus in this case, as in the case first described, the pressure which is initially exerted by the dies upon the work is at substantially exactly diametrically opposite points which thus exerts a maximum tendency of the dies to rotate the work and aids in preventing possible slippage between the dies and the work.

From the above it will be appreciated that in following out the method of the present invention the principal causes which have heretofore existed in the rolling of threads on workpieces. by flat dies and which have resulted in objectionable inaccuracies in threads produced by such method, have been effectively eliminated. In fact, 'threads produced on workpieces in accordance with the present invention are now authorized ior use on all parts capable of being threaded by such dies equally with threads which have heretofore been required to be ground in order to obtain the necessary accuracy in dimensions and surface finish. When it is appreciated that the method of rolling threads in accordance with the present invention requiresno greater time than that required in accordance with conventional practices, and ordinarily less time because of the controllable constant speed of relative appreciated.

In therolllng of threads in accordance with the method of the present invention, as well as in all conventional method employing flat dies, it will be appreciated that in setting up a machine with new dies it is necessary to accurately correlate one of the dies with respect to the other so that the threads produced by the teeth on one of the dies will be synchronized exactly with the threads produced by the teeth on the other of the dies if any semblance of accuracy in the threads of the workpieces formed thereby is to be maintained. The method of rolling such threads in accordance with the present invention provides a method by means of which the accuracy of the setting of the dies may be checked in-a quick and accurate manner so that, if inaccuracies are thus found, the relative positions of the dies may be varied to overcome the same. In accordance with this further phase of the present invention, when a new set of dies is applied to a machine and it is desired to check work blank such as 1 is introduced between the vdies and a partial rotation thereof is eifected,

preferably an amount of rotation less than the one half revolution comprising the minimum amount of rotation during the initial stage of 2,864,442 movement between the dies. As will be appreciated, this forms partial threads in opposite sides of the workpiece but which partial threads preferably do not overlap one another. The workpiece is then removed'from the machine and is helix as the partially formed thread formed by the other die, and if not one or both dies are then shifted to correct the error. While any suitable means may be employed to check the blank with partially formed threads under such circumstances, in accordance with the preferred method the workpiece with the partially formed threads thereon is inserted in an optical projector, indicated diagrammatically at I20 in Fig. 6, with the partially completed thread produced by one of the dies at the top.and the partially completed thread produced by the other of the dies at the bottom, and is adjusted axially until the vertical hair line I22 of the projector is located centrally of a partially completed thread on one side of the workpiece, or centrally of the groove between adjacent partially completed threads of such workpiece. Under such conditions, if the dies are properly located with respect to each other, the hair line I22 will be located centrally of the groove between the threads at the opposite side of the workpiece in the first instance or centrally of a partially completed thread at the diametrically opposite side of the workpiece in the second instance which will thus disclose the accuracy of the setting of the dies. It will be appreciated that, unless the hair line I22 falls in such location, it will indicate that the dies are not properly aligned with each other and the offsetting of the hair line with respect to its proper position in either of the cases mentioned will indicate in which direction one of the dies must be adjusted with respect to the other to 'correct the inaccuracies. One of the dies may then be adjusted in accordance with conventional practice or otherwise with respect to the other thereof to overcome such inaccuracies, the operation may be repeated upon another workpiece and re-checked to determine the accuracy of the adjustment, and such checking and rechecking continued until the final accurate location of one of the die members with respect to the other is definitely established. 'In carrying out this method, after one partially formed thread or groove has been aligned with the hair line I 22, the blank I may be shifted axially until the groove or thread at the opposite side of the blank is aligned with the hair line I22, and the amount of this shifting movement measured accurately by a micrometer or other reading. This will indicate exactly the amount which one die must be shifted vertically with respect to the other'to obtain the required synchronized positions of the dies and aids in eliminating trial. and error methods of attaining the desired results. In such case if means are provided whereby one of the dies may be shifted vertically with respect to the other and such movement is indicated by amicromet-er scale or otherwise, then it will be appreciated that one re-setting will ordinarily be all that is required to correct any inaccuracy that may be found in the relative positioning of the dies. By the above described means it will be appreciated that a quick and accurate method is provided by means of which the accuracy of location of the two die halves with respect to each other may be determined.

' then checked to determine if the partially formed threads formed by one die are in the-same true steps of operation and combinations of steps of operation herein disclosed without departing from the spirit or substance of the broad invention, the scope of which is commensurate with the appended claims.

What I claim is:

1. In the rolling of threads on a substantially cylindrical workpiece between substantially fiat dies having operating surfaces groovedin sectionally complementary relation to the threads desired to be formed on the workpiece, the steps of locating said dies laterally from one another by a distance greater than that required to form the completed thread on the workpiece but less than the diameter of the blank, moving said dies longitudinally with respect to each other and introducing said workpiece therebetween while in said laterally located condition, continuing said longitudinal movement of said dies with respect to each other While they are in said laterally located condition until 'a continuous but incompletely formed thread has been formed on said workpiece, and then moving one die toward the other thereof to reduce the lateral spacing of said dies with respect to each other and continuing said longitudinal movement between said dies.

2. In the rolling of threads on a substantially cylindrical workpiece by means of dies havin substantially fiat operating faces grooved in complementary sectional relationship with respect to the desired threads to be formed on the workpiece, the steps of locating the operative faces of said dies laterally with respect to each other by an amount less than the diameter of the workpiece and greater than the lateral spacing between said dies required to form the completed threads upon said workpiece, moving said dies longitudinally with respect to each other and introducing said workpiece therebetween without substantially varying the lateral spacing of said dies, and then laterally advancing said dies relatively toward one another during continued relative longitudinal movement between them.

8. In the rolling of threads on a substantially cylindrical workpiece by means of dies having substantially flat operating faces grooved in complementary sectional relationship with respect to nal movement between them, and effecting a lateral separating movement between said dies prior to the time said workpiece is ejected therefrom.

4. In the rolling of threads on a substantially cylindrical workpiece by means of dies having substantially flat operating faces grooved in complementary sectional relationship with respect to the desired threads to be formed on the workpiece, the stepsof locating the operative faces of said dies laterally with respect to each other by an amount less. than the diameter of the workpiece and greater than th lateral spacing between said dies required to form the completed threads upon said workpiece, moving said dies itudinally with respect to each other and in- Formal changes may be made in the specific troducing said workpiece therebetween without substantially varying the lateral spacing of said dies, and then. gradually laterally advancing said dies relatively toward one another during continued relative longitudinal movement between them.

5. In the 'rolling of threads on a substantially v cylindrical workpiece by means of dies having substantially flat operating faces grooved'in com,- plementary sectional relationship with respect to the desired threads to be formed on the workpiece, the steps of locating the operative faces of said dies laterally with respect to each other by an amount less than the diameter of the workpiece and greater than the lateral spacing between said dies required to form the completed threads upon said workpiece, moving said dies longitudinally with respect to each other and introducing said workpiece therebetween without substantially varying the lateral spacing of said dies, then advancing said dies relatively toward one another in a'lateral direction until the spacing therebetween is that required to form complete full depth threads in said workpiece during an interval of time required for the workpiece to rotate in excess of one revolutionbetween said (1 es.

6. In the rolling of threads on a substantially cylindrical-workpiece by means of dies having a substantially flat operating faces grooved in complementary sectional relationship with respect to the desired threads to be formed on the work-' piece, the steps of locating the operative faces of said dies laterally with respect to each other by an amount less than the diameter of the workplace and greater than the lateral spacing between said dies required to form the completed threads upon said workpiece, moving said dies longitudinally with respect to each other and introducing said workpiece therebetween without said dies while in said last-mentioned laterally spaced condition until said workpiece has been rotated through at least three additional turns.

substantially varying the lateral spacing of said dies, then advancing said dies relatively toward one another in a lateral direction until the spacing therebetween is that required to form complete full depth threads in said workpiece during an interval of time required for the workpiece to rotate in excess of one revolution between said dies, and continuing said longitudinal movement between said dies while in said lateral advanced relation with respect to each other until said workpiece has rotated through at least three additional turns.-

7. In the rolling of threads on a substantially cylindrical workpiece by means of dies havin piece therebetween until said workpiece has rotated through at least 180 of rotation, then advancing said dies relatively toward one another in a lateral direction during continued longitudinal movement between said dies and over a. period of time required to effect in excess oi one complete revolution of said workpiece between said dies until said dies are laterally spaced from. one another by a distance required to form complete threads on said workpiece, and continuing said relative longitudinal movement betwe n 8. In the rolling of threads on a substantially cylindrical workpiece by means of dies having substantially flat operating faces grooved in complementary sectional relationship with respect tothe desired threads to be formed on the workpiece, the steps of locating said dies in laterally separated relation with respect to each other by a distance equal to from 0.010 to 0.030" less than the diameter'oi' said workpiece, eifectlns relative longitudinal movement-of said dies and introducing said workpiece therebetween, continuing said longitudinal movement of said dies 'after said introduction of said workpiece therebetween until said workpiece has rotated through at least of rotation, then advancing said dies relatively toward one another in a lateral direction during continued longitudinal movement between said dies and over a period of time required to effect in excess of one complete revolution of said workpiece between said dies until said dies are laterally spaced from one another by a distance required to form complete threads on v plementary sectional relationship with respect to the desired threads to be formed on the workpiece, the steps of locating said dies in longitudinally spaced relation with respect to each other suflicient to introduce a workpiece therebetween, locating said dies laterally with respect to each other by a distance less than the diameter of said workpiece but greater than the final lateral spacing of said dies required to form completed threads on said workpiece, introducing said workpiece between the spaced ends of said dies and centrally between the opposed faces of said dies, advancing said dies longitudinally with respect to each other without substantially varying the lateral spacing thereof and effecting an initial grip of said dies upon said work at diametrically opposite points on said work, then continuing to advance said dies longitudinally with respect to each other without substantially varying the lateral spacing thereof until said work has been caused to rotate through at least 180 of rotation, then advancing said dies relatively toward one another in a lateral direction during continued relative movement thereof longitudinally with respect to each other until said dies are imbedded in said work an amount required to form completed threads on said work, and continuing said longitudinal movement of said dies while spaced the last-mentioned distance until said substantially flat operating faces grooved incomplementary sectional relationship with respect to the desired threads to be formed on the workpiece, the steps of introducing said workpiece between said dies while said dies are laterally separated from each other by a distance greater than that required to form ccmpletedjhreads on the workpiece, effecting relative longitudinal movement of said dies and simultaneously advancing said dies relatively toward one another under a pressure capable of being exerted while, and of an extent insufiicient to effect imbedding of the dies to their full extent in the workpiece while, both the dies and the workpiece are stationary, but of sufiicient extent to efiect said imbedding during continued rolling movement of said work relative to said dies. 1

11. In the rolling of threads on a substantially cylindrical workpiece by means of dieshaving substantially flat operating faces grooved in complementary sectional relationship with respect to the desired threads to be formed on the workpiece, the steps of introducing said workpiece between said dies while said dies are laterally separated from each other by a distance greater than that required to form completed threads on the workpiece, effecting relative longitudinal movement of said dies and then urging one of said dies laterally into closerspaced relation with respect to the other thereof during continued longitudinal movement of said dies relative to one another under the influence 'of fluid pressure of insufiicient force to effect complete imbedding of said dies in said work when said dies and work are stationary but suflicient to eifect such complete imbedding during continued relative rotation of said workpiece with respect to said dies.

12. In the rolling of threads on a substantially cylindrical workpiece by means of dies having substantially fiat operating faces grooved in complementarily sectional relationship with respect to the desired threads to be formed on the workpiece, the step of rigidly holding said dies against lateral separating movement while said dies are laterally spaced from one another by a distance less than the outside diameter of said workpiece but greater than the lateral spacing required thereof to form complete threads upon said workpiece, introducing said workpiece between said dies while so spaced and while said dies are moving relative to one another longitudinally thereof, and then laterally advancing said dies relatively toward one another under the influence of fluid pressure of insuflicient extent to completely imbed the grooved faces of said dies into said workpiece when said dies and workpiece are stationary-but oi suflicient intensity to eifect said complete imbedding during continued relative rotation of said workpiece with respect to said dies.

13. In the rolling of threads on a substantially cylindrical workpiece by means of dies having fiat operating faces grooved in complementary sectional relationship with respect to the desired threads to be formed on the workpiece, the method of checking the dies for synchronism with each other comprising the steps of locating the operative faces of said dies laterally with respect to each other by an amount less than the diameter of the workpiece and greater than the lateral spacing between said dies required to form completed threads upon the workpiece, rolling said workpiece between said dies to form partial threads in the workpiece by each of the dies over a substantially no more than half of the circumference of said workpiece, inserting said workpiece in an optical projector, lining up the partial threads formed by one of the dies with a line of the projector perpendicular to the axis of the workpiece, then visually determining the accuracy of location of the partially formed thread on said workpiece produced by the remaining die thereon with respect to said line, and then adjusting at least one of said dies to correct any error thus determined.

JOSEPH H. HOERN. 

